Enhancement of biological nutrient removal process with advanced process control tools in full-scale wastewater treatment plant

Reevaluating the accuracy and specificity of EDTA-based polyphosphate quantification method

Feng et al. (2020) developed a simple, nondestructive, and cost-effective method to quantify polyphosphate (poly-P) in poly-P-accumulating organism (PAO)-enriched sludge samples through 30-h anaerobic exposure to 1 % (w/v) ethylenediaminetetraacetic acid (EDTA). This study optimized the N/P ratio (∼2) of the PAO culture medium in order to provide excess P for poly-P formation in PAO cells. Subsequently, the fluorescence microscopic observation of stained cells confirmed that Corynebacterium glutamicum was a PAO species capable of heterotrophic nitrification. Finally, this study reevaluated the accuracy and specificity of the EDTA-based quantification method, using two confirmed PAO biomass, three confirmed non-PAO biomass, and two sludge samples. The 1 % (w/v) EDTA treatment appears destructive to non-PAO cells, causes the release of other P forms, and is not effective for all PAO species. Under the conditions, the actual P release amount should be calculated by subtracting approximately 8 mg P g-1 total suspended solids from the determination. The amounts of P released from sludge samples was determined not only by the PAO fractions described by Feng et al. but also by PAO community structure and sludge P content.

Prediction of biological nutrients removal in full-scale wastewater treatment plants using H2O automated machine learning and back propagation artificial neural network model: Optimization and comparison

The effective control of total nitrogen (ETN) and total phosphorus (ETP) in effluent is challenging for wastewater treatment plants (WWTPs). In this work, automated machine learning (AutoML) (mean square error = 0.4200 ∼ 3.8245, R2 = 0.5699 ∼ 0.6219) and back propagation artificial neural network (BPANN) model (mean square error = 0.0012 ∼ 6.9067, R2 = 0.4326 ∼ 0.8908) were used to predict and analyze biological nutrients removal in full-scale WWTPs. Interestingly, BPANN model presented high prediction performance and general applicability for WWTPs with different biological treatment units. However, the AutoML candidate models were more interpretable, and the results showed that electricity carbon emission dominated the prediction. Meanwhile, increasing data volume and types of WWTP hardly affected the interpretable results, demonstrating its wide applicability. This study demonstrated the validity and the specific advantages of predicting ETN and ETP using H2O AutoML and BPANN model, which provided guidance on the prediction and improvement of biological nutrients removal in WWTPs.

Trends in Biological Ammonia Production

Food production heavily depends on ammonia-containing fertilizers to improve crop yield and profitability. However, ammonia production is challenged by huge energy demands and the release of ~2% of global CO2. To mitigate this challenge, many research efforts have been made to develop bioprocessing technologies to make biological ammonia. This review presents three different biological approaches that drive the biochemical mechanisms to convert nitrogen gas, bioresources, or waste to bio-ammonia. The use of advanced technologies-enzyme immobilization and microbial bioengineering-enhanced bio-ammonia production. This review also highlighted some challenges and research gaps that require researchers' attention for bio-ammonia to be industrially pragmatic.

Integrated photocatalysis and moving bed biofilm reactor (MBBR) for treating conventional and emerging organic pollutants from synthetic wastewater: Performances and microbial community responses

Increasing concern for emerging organic pollutants (e.g. antibiotics) urges improvements in conventional biological wastewater treatment processes. This study examined the performance of an integrated photocatalysis and moving bed biofilm reactor (MBBR) system in treating synthetic wastewater containing sulfamethoxazole (SMX). It was found that the integrated system could remove over 80.5 % of SMX and 67.7-80.7 % of chemical oxygen demand (COD) with a hydraulic retention time of 24 h. The introduction of photocatalysis had no impact on COD removal and significantly enhanced SMX removal. High-throughput analysis indicated that microbial community greatly altered due to photocatalytic oxidation stress, with clostridiaceae and enterobacteriaceae becoming dominant families. Nevertheless, microorganisms maintained metabolic activity, which may be ascribed to the protection of carriers and microbial self-preservation by secreting extracellular polymeric substances and antioxidant enzymes. Collectively, this study sheds light on treating wastewater containing conventional and emerging organic pollutants by integrating photocatalysis with MBBR.

Potential of food waste-derived volatile fatty acids as alternative carbon source for denitrifying moving bed biofilm reactors

Fossil-based materials such as methanol are frequently used in the denitrification process of advanced biological wastewater treatment as external carbon source. Volatile fatty acids (VFAs) produced by anaerobic digestion of food waste, are sustainable compounds with the potential to act as carbon sources for denitrification, reducing carbon footprint and material costs. In this study, the effectiveness of food waste-derived VFAs (AD-VFA) was investigated in the post-denitrification process in comparison with synthetic VFA and methanol as carbon sources. Acetic acid had the highest rate of disappearance among single tested VFAs with a denitrification rate of 0.44 g NOx-N removed/m2/day, indicating a preferential utilization pattern. While AD-VFA had a denitrification rate of 0.61 mg NOx-N removed/m2/day, sVFA had a rate of 0.57 mg NOx-N removed/m2/day, indicating that impurities in AD-VFA did not play substantial role in denitrification. AD-VFA proved to be promising carbon source alternative for denitrification in wastewater treatment plants.

Removal of persistent organic pollutants and disinfection of pathogens from secondary treated municipal wastewater using advanced oxidation processes

An affordable and sustainable tertiary treatment is imperative to solve the secondary contamination issues related to wastewater reuse. To decontaminate and disinfect the actual secondary treated wastewater, various types of advanced oxidation processes (AOPs) have been studied. The optimization of the oxidant and catalyst is carried out to identify the best-performing system. Under selected experimental conditions, UV/peroxymonosulfate (PMS), O₃/PMS, UV/MnO₂, O₃/MnO₂, UV/O₃/H₂O₂, O₃/MnO₂/H₂O₂, UV/MnO₂/H₂O₂, and UV/O₃/MnO₂ has been identified as an efficient treatment option for simultaneous decontamination (>90% COD removal) and disinfection (100% inactivation of the total viable count of bacteria). The techno-economic assessment revealed that UV/MnO₂ (23.5 $ kg^-1 of COD) UV/O₃/MnO₂ (37.4 $ kg^-1 of COD), UV/H₂O₂/MnO₂ (36.4 $ kg^-1 of COD), and O₃/MnO₂/H₂O₂ (32.5 $ kg^-1 of COD) are comparatively low-cost treatment processes. Overall, UV/MnO₂, UV/H₂O₂/MnO₂, and O₃/MnO₂/H₂O₂ are the three best treatments. Nevertheless, further investigation on by-product and catalyst toxicity/recovery is needed. The results showed that AOPs are a technologically feasible treatment for simultaneously removing persistent organic pollutants and pathogens from secondary treated wastewater.

Hydrogen production from urea in human urine using segregated systems

Removal of nitrogen compounds through biological processes represents the highest energy consumption in conventional centralised wastewater treatment facilities. Alternatively, segregated systems, where wastewater is treated at its source, present the potential to provide value to nitrogen-rich compounds contained in wastewater like urea. This paper demonstrates the feasibility of a novel process to recover energy from human urine based on the pre-isolation of urea to decrease the energy requirements for its thermal decomposition compared to the conventional thermal treatment when in solution, followed by its decomposition into hydrogen. Herein, urea is separated from an aqueous solution by adsorption onto activated carbon. Thermal urea desorption and decomposition into ammonia and CO₂ at 250 °C leads to full regeneration of the carbon, showing a constant adsorption capacity for at least 5 consecutive adsorption/desorption cycles. Finally, when the regeneration and urea decomposition step is coupled to an ammonia decomposition catalyst, hydrogen is produced to be used as an energy fuel. This process opens the door to a new way of circular economy by energy recovery from hydrogen-rich components in segregated wastewater streams. Preliminary energy balances show that the adoption of this energy recovery system in a city of 160,000 inhabitants would lead to a daily hydrogen production of 430 kg, with a net energy production of 2,500 kWh/day. In addition, such waste-to-energy process would lead to energy savings of 4,600 kWh/day in a conventional wastewater treatment plant reducing its energy consumption by around 35%.

Enhancement of sewage sludge thickening and energy self-sufficiency with advanced process control tools in a full-scale wastewater treatment plant

On their path to becoming sustainable facilities, it is required that wastewater treatment plants reduce their energy demand, sludge production, and chemical consumption, as well as increase on-site power generation. This study describes the results obtained from upgrading the sludge line of a full-scale wastewater treatment plant over 6 years (2015-2021) using three advanced process control strategies. The advanced process control tools were designed with the aim of (i) enhancing primary and secondary sludge thickening, (ii) improving anaerobic digestion performance, and (iii) reducing chemical consumption in the sludge line. The results obtained show that the use of advanced process control tools allows for optimising sludge thickening (increasing solids content by 9.5%) and anaerobic digestion (increasing both the removal of volatile solids and specific methane yield by 10%, respectively), while reducing iron chloride and antifoam consumption (by 75% and 53%, respectively). With the strategies implemented, the plant increased its potential energy self-sufficiency from 43% to 51% and reduced de-watered sludge production by 11%. Furthermore, the upgrade required a low investment, with a return of capital expense (CAPEX) in 1.98 years, which presents a promising and affordable alternative for upgrading existing wastewater treatment plants.

Introducing bioflocculation boundaries in process control to enhance effluent quality of high-rate contact-stabilization systems

High-rate activated sludge (HRAS) systems suffer from high variability of effluent quality, clarifier performance, and carbon capture. This study proposed a novel control approach using bioflocculation boundaries for wasting control strategy to enhance effluent quality and stability while still meeting carbon capture goals. The bioflocculation boundaries were developed based on the oxygen uptake rate (OUR) ratio between contactor and stabilizer (feast/famine) in a high-rate contact stabilization (CS) system and this OUR ratio was used to manipulate the wasting setpoint. Increased oxidation of carbon or decreased wasting was applied when OUR ratio was <0.52 or >0.95 to overcome bioflocculation limitation and maintain effluent quality. When no bioflocculation limitations (OUR ratio within 0.52-0.95) were detected, carbon capture was maximized. The proposed control concept was shown for a fully automated OUR-based control system as well as for a simplified version based on direct waste flow control. For both cases, significant improvements in effluent suspended solids level and stability (<50-mg TSS/L), solids capture over the clarifier (>90%), and COD capture (median of 32%) were achieved. This study shows how one can overcome the process instability of current HRAS systems and provide a path to achieve more reliable outcomes. PRACTITIONER POINTS: Online bioflocculation boundaries (upper and lower limit) were defined by the OUR ratio between contactor and stabilizer (feast/famine). To maintain effluent quality, carbon oxidation was minimized when bioflocculation was not limited (0.52-0.95 OUR ratio) and increased otherwise. A fully automated control concept was piloted, also a more simplified semiautomated option was proposed. Wasting control strategies with bioflocculation boundaries improved effluent quality while meeting carbon capture goals. Bioflocculation boundaries are easily applied to current wasting control schemes applied to HRAS systems (i.e., MLSS, SRT, and OUR controls).

Biological nutrients removal performance under starvation stress: Efficacy deterioration and recovery

Biological nutrients removal performance affected by starvation stress was investigated via the addition of pre-anoxic stage to SBR. COD removal efficiency maintained at around 90% regardless of the starvation stress. Starvation stress presented significant impact on nitrogen and phosphorus removal, with noticeable reduction of TN removal and remarkable deterioration of TP removal as prolonging the pre-anoxic time, which was mainly attributed to the integrative effect of carbon source competition, depression of denitrification and invalid P release as well as the variation of microbial community. It was notable that starvation stress exerted distinct evolution on microbial community. The improvement in relative abundance of the certain genera relating to denitrification was the main reason for the partial recovery of nitrogen removal after eliminating stress starvation. The promotion of P uptake capacity accompanied with the relief of invalid P release and the enriched DPAOs accounted for the complete recovery of phosphorus removal.

Potential of anaerobic co-fermentation in wastewater treatments plants: A review

Fermentation (not anaerobic digestion) is an emerging biotechnology to transform waste into easily assimilable organic compounds such as volatile fatty acids, lactic acid and alcohols. Co-fermentation, the simultaneous fermentation of two or more waste, is an opportunity for wastewater treatment plants (WWTPs) to increase the yields of sludge mono-fermentation. Most publications have studied waste activated sludge co-fermentation with food waste or agri-industrial waste. Mixing ratio, pH and temperature are the most studied variables. The highest fermentation yields have been generally achieved in mixtures dominated by the most biodegradable substrate at circumneutral pH and mesophilic conditions. Nonetheless, most experiments have been performed in batch assays which results are driven by the capabilities of the starting microbial community and do not allow evaluating the microbial acclimation that occurs under continuous conditions. Temperature, pH, hydraulic retention time and organic load are variables that can be controlled to optimise the performance of continuous co-fermenters (i.e., favour waste hydrolysis and fermentation and limit the proliferation of methanogens). This review also discusses the integration of co-fermentation with other biotechnologies in WWTPs. Overall, this review presents a comprehensive and critical review of the achievements on co-fermentation research and lays the foundation for future research.

Calcium hypochlorite enhances the digestibility of and the phosphorus recovery from waste activated sludge

Waste activated sludge (WAS) can be treated using anaerobic digestion (AD) for biogas recovery and volume reduction. However, the poor digestibility and hydrolysis of WAS limit AD applications. The current study investigated the feasibility of applying calcium hypochlorite as a WAS pretreatment strategy to improve AD treatment efficiency using laboratory reactors. The results showed that pretreatment with 5 - 20% Ca(ClO)₂ (total suspended solids basis) significantly enhanced WAS anaerobic digestibility, and led to significantly enhanced methane production rate and biomethane yield comparing to the AD of raw WAS (P < 0.05). Low Ca(ClO)₂ pretreatment (5 - 10%) significantly enhanced digestion efficiency, which can be attributed to the development of fermentative and syntrophic bacteria. However, high Ca(ClO)₂ doses (>20%) reduced microbial activities, leading to slow release of dissolved organic compounds and prolonged methane production lag phase. In addition, high Ca(ClO)₂ removed 82.7% of the initial phosphate by calcium-phosphate binding, reducing the phosphorus in liquid digestate.